This invention is directed to wooden pallets for material transport which are handled with forklift trucks, and to their method of manufacture. More particularly, the invention is directed to pallets comprising deckboards nailed to vertically disposed stringers which are reinforced and adapted to help position and retain cargo thereon.
Pallets are used in ever-increasing number in commerce to transport virtually all types of merchandise. These pallets when loaded with merchandise almost by necessity are handled with forklift trucks. When empty, however, they can be handled with forklift trucks, but oftentimes are manually stacked or moved manually from one location to another. Pallets, therefore, while of simple design must meet numerous specifications, many of which are conflicting.
More specifically, pallets since they are a service item must be relatively inexpensive. To be inexpensive, they must be made of materials of relatively low cost and must be fabricated in a manner which will make most effective use of labor. Since the pallets are at times handled manually and since they are shipped from place to place with merchandise, they must be relatively light in weight in addition to having high structural strength. Most pallets, therefore, are made of wood and comprise vertical stringers with transverse deckboards nailed thereto, top and bottom. To facilitate handling with forklift trucks, the pallets preferably are designed for pick up from the sides as well as from the ends of the pallet, i.e., a so-called four-way pallet as opposed to a two-way pallet if pick up is from the ends only; and, accordingly, the stringers are notched for entrance of the fork of the forklift truck. In construction, after cutting to proper length and notching, the stringers are fed to automatic stringer "feed boxes," with the deckboards then being applied and nailed with nail handguns or automatic nailers.
In spite of the acceptance of wood as the logical choice of material for pallet construction, pallets constructed from wood are subject to damage or breakage due to heavy loading and in being subjected to substantial mechanical impact from the fork end of the forklift truck due at times to simple operator carelessness or indifference. Breakage in pallets occurs most often at the end of the stringers and, if the stringers are notched, substantially immediately adjacent to the notch. In order to reduce breakage and to increase the strength of wood pallets, various modifications to pallets have been suggested including incorporating metal braces between the stringers and deckboards; applying metal bands to the pallets at strategic points; using reinforcing nails pounded into the stringers, as well as constructing the pallets with bolts extending through the stringer and deckboards. These efforts have been unacceptable to large users for various reasons. Metal braces and metal bands applied to the pallets not only increase material cost and at times make the pallets unacceptably heavy, but also increase labor costs during the course of construction and in large measure preclude the use of conventional automatic stringer feed boxes and nailing machines. Moveover, a pallet containing the metal braces and/or bands is difficult to repair once damaged since the conventional method of cutting the nails between the deckboards and stringers or otherwise conventional methods of pulling the nails connecting the deckboards and stringers cannot be conveniently employed. Nail reinforcement, while providing some improvement, has been limited by the lack of rigidity provided by reinforcement with relatively flexible nails driven into the stringer. Bolts extending through the stringers and deckboards, while improving structural integrity, again greatly increase cost both from the standpoint of initial construction and repair. In the initial construction it is necessary to drill the deckboards and stringers in substantially perfect alignment and then insert the bolts. In order to avoid having boltheads or nuts interfere with the stacking of merchandise on the pallets and/or interfering with the setting down of the pallets and/or damaging merchandise when one loaded pallet is placed on another loaded pallet, the boltheads and nuts must be countersunk to provide a flush surface. This further increases the cost of the manufacturing operation and also requires the use of relatively thick deckboards for adequate strength. The countersinking of the boltheads into the deckboards also provides a weakened area at the point of countersinking, causing the deckboards to break at the weakened point.
Application Ser. No. 796,652 filed May 13, 1977 discloses pallets constructed from deckboards nailed to stringers which may be notched or unnotched and include a metal pin or a pin of another material having structural strength greater than that of wood between the end and notch of conventionally use stringers or at the ends of the stringer. The pin is completely embedded within the stringer. In fabrication of the improved pallet, the stringers are cut to proper length and, if a four-way pallet, notched as conventionally done. However, the stringers are then drilled in the vertical direction either completely through or substantially through and a pin inserted. The pins are embedded and positioned in the stringer so as not to interfere with the nailing of deckboards with automatic nailers or the like. The stringers with the pins inserted are then used in the fabrication of the pallet in a conventional manner as, for example, by feeding the stringers into automatic stringer feed boxes and applying the deckboards, top and bottom, with nail handguns or automatic nailers.
Copending application Ser. No. 796,652 filed May 13, 1977 now abandoned also discloses the use of a U-shaped rod running lengthwise of the stringer, extending over the notched portions of the stringer with the ends of the U extending vertically down into the stringer. The rod is fitted into a groove in the stringer so as not to interfere with deckboard placement.
As a still further embodiment, Ser. No. 796,652 filed May 13, 1977 discloses the use of U-shaped rods extending endwise from stringer to stringer of the pallet and extending vertically downward into the stringer. This embodiment provides improved structural strength to the pallets and, further, helps to hold the stringers of the pallet in squared relation, decreasing the stress on the deckboards.
The pallets made in accordance with the disclosure of Ser. No. 796,652 have greatly improved strength particularly at the ends of the pallet or stringer adjacent to the notch where notched pallets are most often damaged by being struck with the fork end of a forklift truck or the like. The structural strength of the pallets is fully equivalent or greater than the structural strength of pallets using deck bolts or rods. However, unlike with the use of bolts and rods, the pallets can be rapidly constructed using conventional automated equipment and can be repaired in a conventional manner since the pins, being fully enclosed within the stringer, for purposes of working the pallet are as if not there. Moreover, an advantage over the use of bolts is that there is no weakening of the deckboards through drilling and countersinking of boltheads, or the like. Of equal or greater importance, however, is that when a pin-reinforced stringer is struck by the tines of a forklift truck the pin, although not preventing the splitting of the stringer which is a virtual impossibility, arrests or stops the splitting or cleaving of the stringer end substantially at the pin. Although the stringer is cleaved and in part separated, the relative movement between the steel pin and the wooden stringer permits the forcing together of the separated stringer parts by pounding or the like and the pallet retained in normal service.